Fascinated by his amphibious gift, Wallace painted a watercolor of the flying frog, then an unknown species. He later discussed the species, named Rhacophorus nigropalmatus or “Wallace’s frog,” as an example of evolution’s stepwise process in his 1869 book The Malay Archipelago, in which he included a woodcut based on his original frog painting: “[I]t is very interesting to Darwinians as showing that the variability of the toes which have been already modified for purposes of swimming and adhesive climbing, have been taken advantage of to enable an allied species to pass through the air like the flying lizard.”

But at the time he first laid eyes on the frog, Wallace would not have called himself a “Darwinian,” though the two had met and corresponded. Indeed, there was no such term in 1855. Earlier that year, Wallace had holed up for the rainy season in a small house in Borneo’s Sarawak region to rest, recuperate from his exertions in the field, and write. It was there that Wallace produced his famous “Sarawak Law” paper, in which he articulated the idea that geography is related to the distribution of species, with natural barriers like mountains and bodies of water giving rise to closely related but separate species. Furthermore, he noted, new species arise from existing ones, branching off from each other like new limbs on a tree.

Although Wallace had been interested in the idea of evolution since 1845, the Sarawak Law paper, published in September 1855, “was his first real attempt to promote his evolutionary views,” says George Beccaloni, curator of cockroaches and related insects at the Natural History Museum in London and director of the Wallace Correspondence Project.

Three years later, in 1858, Wallace and Charles Darwin jointly published a landmark paper outlining the theory of evolution by natural selection. Around the same time, Wallace was preparing notes for a book on evolution. “If you compare his ideas with Darwin’s notes, they’re incredibly alike,” Beccaloni says. But that book was never published. Wallace abandoned it when Darwin released On the Origin of Species, a decision that meant Wallace received relatively little recognition in the 20th century, when interest in Darwin’s ideas surged.

But with the recent rediscovery of a collection of Wallace’s paintings and sketches from the Malay Archipelago—including the original watercolor of the flying frog—and the publication of his correspondence with Darwin and others, Wallace’s contributions to science will, Beccaloni hopes, likewise become less obscure. “It will take quite a few years, but hopefully we’ll start getting people to look at Wallace more seriously and in more detail, and hopefully eventually he’ll get the recognition he deserves,” he says.